Steam generating unit



Nov. 29, 1960 Filed May 19, 1958 N. s. BLoDGT'r STEAM GENERATING UNIT IOM. /4

Ill'I 3 Sheets-Sheet 1 Nov. 29, 1960 Filed May 19, 1958 N. s. BLODGETT STEAM. GENERATING UNH 5 Sheets-Sheet 2 NOV. 29, 1960 N. s. BLOD'GETT 2,962,006

' STEAM GENERATING UNIT Filed may 19, 1958 s sheets-sheet s United States Patent 'i' 'STEAM GENERATIN G UNIT Norman S. Blodgett, Westboro, Mass., assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts 'Filed May 19, 1958, Ser. N0. 736,180

3 Claims. (Cl. 122-479) This invention relates to control of superheat, and more particularly to apparatus arranged to change the exit temperature of the steam leaving a superheater or to maintain the exit temperature of said steam constant, irrespective of other changes taking place in the steam generating apparatus. This application is a continuationin-part of patent application Serial Number 423,271 'led April- 15, 1954, now abandoned.

"In the past, workers doing research work'on gas turbine nozzles have found that, at gas velocities in excess of the velocity of sound, a heat loss is incurred in the nozzle far in excess of that computed theoretically by theextrapolation of Nusselts formula 'for the heat transfer from gases flowing through tubes. The observation of this phenomenon of unexpectedly high heat transfer, which Ais very much to the disadvantage of gas turbine Aperformance suggested its exploitation in a steam generator designed to operate at exceedingly high gas velocities. A studyk of heat transfer curves obtained from experiments on a test tube connected to a small combustion chamber show that over a range from about 1,000 feet per second to 700'feet per second the heat transfer coeicients actually `obtained are consistently higher than those derived lfrom Nusselts formula, butin the higher velocity range above 1,00() feet per second the difference between the experimental Vvalues and the theoretical values of Nusselt was observed to increase rapidly with the velocity. With regard to heat transfer by radiation, this is likewise greatly increased on account of the increased density of the radiating gas. The original idea of utilizing this greatly increased heat transfer at high gas velocities had been to use an explosion cycle for the combustion of gaseous or liquid fuel with the charging pressure in the explosion chamber supplied by an exhaust driven turbo-blower of which the outward pressure would only have to be about vone-fourth of that occurring at the moment of explosion. The exhaust gas turbine coupled with the compressor was to be passed by the flue gas after this latter had given oif the `greater part of its heat to the evaporator, the superheater, and the economizer. The attempts to use the concept of high heat transfer at high gas velocity was used in the so-called Velox steam generator. However'this generator was not successful, particularly with the burning of pulverized coal as a fuel, because the heavy flyash particles caused extreme abrasion of the heat transfer tubes.

It has been suggested also that heat transfer may be increased by using a pulsed burner such as the so-called Schmidt tube in place of the ordinary fuel burning equipment. The pulsed burning of the'Schmidt tube produced increased heat transfer by superimposing on the general ow of gas a succession of compressions and rarefractions of low frequency and high power. Such installations would be expensive and noisy. Furthermore, the apparatus has not beenperfected tothe point where .it is commercially reliable. My conception involves the use of ordinary burningequipment and to introduce pulsations in the yneighborhood of the superheater by use of a sonic wave generating apparatus. On the other hand the freice quency of the wave may be well above the audible range to obviate noise. The increase in transfer in that case is brought about by the increased frequency of movement of the gas molecules which offset thelower magnitude of displacement of these vibrations. The general ow of gas would not be alfected, but the individual molecules `of gas would be vibrated rapidly, thus giving a heat transfer between the gas and the superheater that would be commensurate with much greater gas velocity, The wave generator, whether sonic or supersonic, would be used adjacent the superheater and, by varying the frequency or magnitude of the sonic wave, the superheat would be controlled. This apparatus will permit vlow ,gas velocities in a pulvenized coal installation, and the heavy flyash particles would not partake of the vibratory movement experienced by the gas molecules. The result in such a case would be vhigh eifective gas velocity without abrasion of the tubes and without the expense of large draft apparatus.

It is therefore an outstanding object of this invention toprovide a method and apparatus for controlling superheat which is inexpensive and reliable.

It is another object of the present invention to provide a method of controlling superheat which involves varying the effective velocity of the gases passing over the superheater, while obviating any difficulties due to abrasionof heat transfer surfaces at high effective velocities.

It is a still further object of this invention to provide an apparatus for controlling superheat which is inexpensive and easy to operate, which can be used in existing installations, and which is effective .with very little time lag.

Another object of the invention is the provision rolf a method and means for controlling superheat which acts directly tofincrease the heat transfer between the furnace gas and the steam inthe superheater.

With these yand other objects in view as will be apparent to those skilled in the art, the invention resides in the method and in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be 4best understood by reference to certain of its structural `forms as illustrated by the `accompanying drawings in which:

Figure 1 is a longitudinal view of a modern steam generating apparatus making use of the philosophy of the present invention,

Figure 2 is a sectional view considerably enlarged of a portion of the apparatus shown in Figure 1,

lFigure 3 is a longitudinal view of a steam generating apparatus shown in Figure 4.

Like reference characters denote similar parts in the several figures of the drawings.

Referring first -to Figure 1, wherein is best shown the general features of the invention, a steam generating unit, designated generally by the reference'numera'l lil, comprises a furnace 11 having a combustion chamberl'lV and a boiler 13 having a steam-and-water drum 14, a-'fue'l feeder 15 is connected to a coal storage bunker, not shown, and to a pulverizer 16. The exit ofthe pulvenizer is connected to burners 17 mounted'on a'front walll of the furnace 11 by means of a conduit 19 and branch conduits 20. The furnace 11 also is provided'with a rear wall 21 and side Walls 22. The front and rear Walls converge to form ahopper 23 in the lower portion of the combustion chamber. A header i24-is situated adjacent the-apex of the hopper 23 and is provided 4with Water from the steam-and-Water drum 114 bymeans of-downcomers, not shown. The walls of the furnace are substantially covered with tubes which radiateupwardly from thefheader 24 and converge againy on the steam-and-water `drum 14. VA vertical b'ackpass 25' is provided rearwardly of the rear wall 21 and in this pass resides a primary superheater 26, an economizer 27, and an air heater 28. A breeching 29 leaves the air heater and carries exhaust gases to a stack, not shown. A duct 29` leaves the air heater and is connected to the burners 17 to supply them with preheated air. A convection superheater 30 resides in the upper portion of the combustion chamber and is screened from radiation by a refractory wall 31. Across the top of the combustion chamber is a -roof 32 in which is mounted adjacent the superheater a wave generator 33 of the pulsating burner type, which will be more fully described hereinafter. A duct 34 is connected from the duct 29 to the wave generator 33 to supply it with preheated air. A duct 35 is connected to the conduit 19 and to the wave generator to supply it with pulverized coal. A control valve 36 is interposed in the condu-it 34 and a similar control valve 37 is inserted in the conduit 35. Actuators 38 and 39, which may be of the hydraulic cylinder type, are connected to the valves 36 and 37, respectively, to determine the setting thereof. The actuators 38 and 39 are connected by control lines to a controller 40. The controller 40 is in turn connected to a measuring instrument 41 which resides in a steam exit header 42 to which the superheater 30 discharges superheated steam for use. The measuring device 41 may be of the gas-pressure type which transmits to the controller 40 a gas pressure indicative of the temperature of the steam in the header 42.

Referring to Figure 2, which shows the detailed construction of the wave generator 33, it can be seen that the wave generator is pulsating burner which res downwardly through an opening 43 in the roof 32 of the furnace. The water tubes lining the roof 32 are suitably bent so that they do not cross the opening 43. The wave generator 33 comprises a housing 44 which has a restricted exit overlying the opening 43. The entrance end of the housing 44 is provided with a valve seat 45 in which is positioned a valve 46 which is spring-biased into position against the seat, the valve 46 being mounted on a suitable spider 47 fastened in the housing 44. A manifold 48 surrounds the inlet end of the housing 44 and the fuel conduit 35 and the air conduit 34 are connected thereto. The housing 44 is of a generally prolatespheroidal shape and the valve 46 is arranged coaxially therewith. Furthermore, the fuel conduit 35 is arranged coaxially of the housing 44 and its end, which extends well into the manifold 48, is provided with a coal spreader 49.

The operation of the apparatus will now be clearly understood in view of the above description. Feedwater entering the steam generating unit passes through the economizer 27 and enters the steam-and-water drum` 14. It passes from there to the header 24 and is distributed through the waterwall tubes and rises upwardly along the walls of the combustion chamber. At some point in the travel of the water, it is converted into steam and discharged into the steam-and-water drum 14. From the steam-andwater drum 14 it passes into the primary superheater 26 and from there to the secondary superheater 30. It is to be noted that the steam in passing through the superheater 30 passes initially in the same direction as the hot gases, but then is caused to pass in counterow to the hot gases before entering the header 42. The fuel entering the steam generating unit 10 is passed into the pulverizer 16 by means of the feeder 15 and is converted to a fine pulverized state. It enters the conduit 19 and eventually arrives at the burners 17. In the meanwhile, combustion air passes through the air heater 28 into the conduit 29 where it is distributed also to the burners 17. The fuel and air combine in the combustion chamber 12 with the resultant formation of hot gases of combustion which transmit heat by radiation and convection to the heat exchange surfaces of the steam generating unit. Combustion is completed before the gases leave the combustion chamber 12 and enter the upper pass in which the superheater 30 is located. At certain times it is necessary to restrict the tiow of fuel and air to the burners 17 in order, for instance, to form less steam in the header 42 at a time when less steam is needed. This means that there is a smaller flow of products of combustion over the surface of the superheater 30 and this will result in a 'lower superheat temperature in the header 42. The wave generator 43 is brought into play to correct this situation and cause the superheat of the steam in the header 42 to remain constant. To begin with, fuel entering the wave generator through the conduit 35 and air entering through the conduit 34 combine in the manifold 48 and are permitted to enter the housing 44 through the valve 46. The fuel-air mixture -is burned in an explosive manner within the housing 44 and at the moment of the explosion a strong compressive wave is projected into the area surrounding the superheater 30. This sudden increase in pressure in the housing 44 causes the valve 46 to close so that no further fuel and air can enter the housing 44. However, once the explosion is over a rarefaction in pressure occurs, both within the housing 44 and within the area surrounding the superheater 30. This rarefaction or drop in pressure causes the valve 46 to open, thus admitting more fuel and air. In this way the wave generator 33 produces a series of compressions and rarefactions in the area in the body of gas surrounding the superheater 30. In addition, of course, hot products of combustion are ejected from the wave generator and join the body of gases originating in the combustion chamber 12. The presence of compressions and rarefactions n the body of gas surrounding the superheater 30 causes the individual gas molecules to vibrate or to move back and forth in a manner entirely distinctive from the general flow of gases through the superheater. In other words, each individual gas particle is subject to a general movement due to the draft through the steam generating unit and is also subject to a small to and fro movement superimposed upon the general flow movement. When i the frequency of the wave generator is selected properly,

this vibratory movement of the individual gas particles is such that the particles of yash and the like which may exist in the gas flow do not so move because of their tremendous inertia compared to the mass of the individual i gas molecules. The abrasive effect on the superheater for instance, to a change in load, this fact is signalled by the measuring device 41 to the controller 40. The controller takes the proper action and causes the actuators 38 and 39 to change the settings of the valves 36 and 37 controlling the ilow of fuel and air to the wave generator 33. The change in the rate of ow of fuel and air to the wave generator will cause a corresponding change in the frequency of the compressions and rarefactions. This, in turn, will produce a corresponding change in the rate of heat transfer to the superheater and thus will correct the temperature of superheated steam in the header 42 which is the result to be desired.

In Figure 3 is shown another embodiment of the invention used in conjunction with a steam generating unit 55) having a furnace 51 including a combustion chamber 52. A boiler 53 is provided with a steam-and-water drum 54. A feeder 55 is connected through a pulverizer 56 to burners 57 mounted in the front wall 58 of the furnace 51 by means of a conduit 59 and branch conduits 60. The furnace 51 also has a rear wall 61 and side walls 62. The front and rear walls converge to form a hopper 63 in the lower portion of the combustion chamber 52. The steam-and-water drum is connected by downcomers, not shown, to headers 64 and 65 in the lower portion of the hopper 63. The -waterwall tubes lining the walls of the combustion chamber extend upwardly from these headers. Behind the rear wall 61 of the furnace is a backpass containing a primary superheater 66, an economizer 67, and an air heater 68. A convection superheater 70 is situated in the upper portion of the furnace and is protected from radiation by a refractory wall 71. The superheater 70 discharges into the superheater header 72 and is of the combined radiation-convection type. A roof 73 is provided in the upper portion of the combustion chamber 52 and on this roof is mounted a wave generator 74 connected by control w-ires 75 and 76 to a contro-ller 77. A temperature measuring device 78 is mounted in the header 72 and is connected by control wires 79l and 80` to the controller 77.

Referring to Figure 4, which shows more specilically the construction of the wave generator 74, it can be seen that the roof 73 is provided with an opening 8,1 over which the wave generator is mounted. The wave generator 74 is of the electrical type having a suitable heat resistant diaphragm S2 overlying the opening 81 and being the only portion of the wave generator 74 which is exposed to the radiant heat of the furnace. A suitable core 83 is fastened to the central portion of the diaphragm and extends upwardly and is surrounded by a coil 84 which terminates in the control wires 75 and 76 extending to the controller 77. A conical housing 85 surrounds these elements and holds them in place and an insulating jacket 86 surrounds the housing. The controller 77 may be selected from any one of many types in which a signal -introduced at the input terminals brings about a functional change in the signal which appears on the output terminals.

In operation, this embodiment of the invention is very similar to the first one described. When the temperature of steam in the header 72 changes for any reason such as change in load, the temperature measuring device 78 indicates this and sends a signal along the control wires 79 and 80 to the controller 77. This serves to change the current in the control wires 75 and 76 emanating from the controller 77 and thus changes the current in the core 84. In the preferred embodiment the controller 77 transmits an alternating or pulsating signal to the wave generator 74, thus causing a corresponding movement of the diaphragm 82. Vibration of the diaphragm 82 causes corresponding compressions and rarefactions in the body of gas surrounding the superheater and thus changes the amount of heat ltransfer from the gas to the steam and changes the temperature of superheated steam in the header 72 to a pre-selected value.

Although in the above description it has been stated that the wave generators in the two embodiments serve to control the heater transfer tothe superheater by means of changes in the frequency of compression and rarefaction in the body of gas surrounding the superheater, it is to be realized that a similar change may be made by controlling the intensity of the compressions and rarefactions. Furthermore, it is possible that both of these factors may be changed; that is to say, that the superheat may be controlled by changes in the frequency and in the intensity of the signals transmitted to the body of gas surrounding the superheater.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to conline the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An apparatus for controlling superheat in a steam generating unit having a combustion chamber, a convection gas passage extending away from the chamber, a tubular superheater comprising a plurality of tubes extending transversely of the ow of gas in the passage, a wave generator means in the gas passage adjacent the superheater superimposing on the general ow of gases through the passage and the superheater a series of very high frequency compressions and rarefactions, temperature means connected to the superheater for measuring the output temperature of the superheated steam, controller means connected to the temperature means and to the wave generator means, the temperature means actuating the controller means to cause the latter to change the frequency of compressions and rarefactions upwardly and downwardly in'response respectively to downward and upward changes in the temperature of the superheated steam to increase and decrease the motion of the gas particles to increase and decrease the rate of transfer of heat to the superheater because of a corresponding change in the motion of the gas particles relative to the tubes.

2. An apparatus for controlling superheat in a steam generating unit, comprising a combustion chamber, a convection gas passage extending away from the chamber, a tubular superheater comprising a plurality of tubes extending transversely of the ow of gas in the passage, a wave generator means in the gas passage adjacent the superheater superimposing on the general ow of gases through the passage and the superheater a series of very high frequency compressions and rarefactions, temperature means connected to the superheater for measuring the output temperature of the superheated steam, controller means connected to the temperature means and to the wave generator means, the temperature means actuating the controller means to cause the latter to change the intensity of the compressions and rarefactions upwardly and downwardly in response respectively to downward and upward changes in the temperature of the superheated steam to increase and decrease the motion of the gas particles to increase and decrease the rate of transfer of heat to the superheater because of a corresponding change in the motion of the gas particles relative to the tubes.

3. An apparatus for controlling superheat in a steam generating unit comprising a combustion chamber, a convection gas passage extending away from the chamber, a tubular superheater comprising a plurality of tubes extending transversely of the ow of gas in the passage, a wave generator means in the gas passage adjacent the superheater superimposing on the general ow of gases through the passage and the superheater a series of very high frequency compressions and rarefactions, temperature means connected to the superheater for measuring the output temperature of the superheated steam, controller means connected to the temperature means and tothe wave generator means, the temperature means actuating the controller means to cause the latter to change a quality of the compressions and rarefactions upwardly and downwardly in response respectively to negative and positive diierences between the temperature of the superheated steam and a pre-selected reference temperature to increase and decrease the motion of the gas particles, thus producing an increase and decrease in the rate of heat transfer from the gases to the steam in the superheater because of a corresponding change in the motion of the gas particles relative to the tubes to Ireturn the output temperature to the preselected value.

Power Generation, pages 86, 88, 132, 136, and 138, September 1948. 

